Fourteen months into a campaign that has the feel of a movement, Illinois Sen. Barack Obama has collided with the gritty political traditions of Philadelphia, where ward bosses love their candidates, but also expect them to pay up.

The dispute centers on the dispensing of "street money," a long-standing Philadelphia ritual in which candidates deliver cash to the city's Democratic operatives in return for getting out the vote.

Flush with payments from well-funded campaigns, the ward leaders and Democratic Party bosses typically spread out the cash in the days before the election, handing $10, $20 and $50 bills to the foot soldiers and loyalists who make up the party's work force. It is all legal -- but Mr. Obama's people are telling the local bosses he won't pay.

That sets up a culture clash, pitting a candidate who promises to transform American politics against the realities of a local political system important to his presidential hopes. Pennsylvania holds its primary April 22.

Mr. Obama's posture confounds neighborhood political leaders sympathetic to his cause. They caution that if the senator withholds money that gubernatorial, mayoral and presidential candidates have willingly paid out for decades, there could be defections to New York Sen. Hillary Rodham Clinton. And the Clinton campaign, in contrast, will oblige by forking over the money, these ward leaders predict.

"We've heard directly from the Obama organizer who organizes our ward, and he told us it's an entirely volunteer organization, and that I should not expect to see anything from the Obama campaign other than ads on TV and the support that volunteers are giving us," said Greg Paulmier, a northwestern Philadelphia ward leader.

Neither the Clinton nor the Obama campaign would say publicly whether it would comply with Philadelphia's street-money customs. But an Obama aide said Thursday that it had never been the campaign's practice to make such payments. Rather, the campaign's focus is to recruit new people drawn to Mr. Obama's message, the aide said.

The field operation "hasn't been about tapping long-standing political machinery," the aide said.

Carol Ann Campbell, a ward leader and Democratic superdelegate who supports Mr. Obama, estimated that the amount of street money that Mr. Obama would need to lay out for election day is $400,000 to $500,000.

"This is a machine city, and ward leaders have to pay their committee people," Ms. Campbell said. "Barack Obama's campaign doesn't pay workers, and I guarantee you if they don't put up some money for those street workers, those leaders will most likely take Clinton money. It won't stop him from winning Philadelphia, but he won't come out with the numbers that he needs" to win the state.

A neutral observer, state Rep. Dwight Evans, whose district is in northwest Philadelphia, said there might be a racial subtext to the dispute. Ward leaders, said Mr. Evans, a former ward leader who is black, see Mr. Obama airing millions of dollars' worth of television ads in the city -- money that benefits largely white station owners, feeding resentment. People wonder why Mr. Obama isn't sharing the largess with the largely black field workers trying to get him elected, he said.

Hardscrabble neighborhoods across the city have come to depend on street money as a welcome payday for knocking on doors, handing out leaflets and speaking to voters as they arrive at polling places.

Peter Wilson, a ward leader from West Philadelphia, said: "Most of the ward leaders, we live in a very poor area, and people look forward to election days. ... People are astute. They know the Obama campaign has raised millions of dollars."

Street money is also an enduring political practice in Chicago, Baltimore, Newark, N.J., and Los Angeles.

It is unclear to what extent Mr. Obama could suffer at the polls if any part of the city's Democratic apparatus jumps to Mrs. Clinton. Mr. Obama's strategy in Pennsylvania depends on a strong turnout in the city's black precincts. That way, he can cut into the advantage that Mrs. Clinton has among older and blue-collar voters elsewhere in the state.

Ms. Campbell, who heads a coalition of black ward leaders, said she could not in good conscience ask people to work for Mr. Obama for free. "I'm not going to do that," she said. "There are a lot of poor people here."

Mr. Paulmier said that of his ward's 48 committee people, the vast majority support Mr. Obama. Although he doesn't expect a wholesale exodus to the Clinton campaign if no street money is paid, a handful of those key people might bolt, he said.